Truly care about her.
Sincerely listen to her, talk to her.
Pay attention to her body language.
Remember to try to please her five senses: Sight, hearing, smell, taste, touch.
Remember to try to use her five love languages: Acts of service, receiving gifts, quality time, words of affirmation, physical touch.
Spend time with her.
Do all sorts of activities with her (particularly, maybe, those you know she likes, but also getting out of her comfort zone,
discovering activities with her or making her discover activities (scientific, artistic, social, exercise/sport).
Help her become the best woman, person she can be (self-actualization).
Cuddle, curl up, huddle, nestle, nuzzle, snuggle with her.
Hug, kiss her.
Think poetry, romance.
Play games with her.
Offer her, at times, a simple handmade, personal gift (it can be prose, a little story, a poem, a drawing, a musical composition, etc.).
You can hardly sincerely say too often “I miss you”, “I think of you”, “You’re intelligent, talented, beautiful”, “I love you”.
Touch on, venture with her into philosophy (aesthetics, ethics, political philosophy, etc), history, law, political science, economics, biological and physical sciences, psychology, literature, cultures of other people, cooking, languages, role playing, theater, music (classical, popular, rock and roll, etc), dance (social dance, Latin American dances, Argentine tango, folkloric dance, slows, etc), drawing, painting, sculpture, photography, movie.
Have fun, laugh, be playful, teasing with her.
And then ask her: Did we forget something? Ohhh… (Wink!)